Door knocker



FIG. 1 is a perspective view of a door knocker showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a right side elevational view thereof, the left side being a mirror image;

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a door knocker, substantially as shown and described. 